This invention relates generally to improvements in an electrostatic apparatus, and more specifically, to improvements in the development stations of an electrostatic image-forming apparatus using liquid development toner and photoconductors which have low electrical potentials.
Electrostatic apparatuses of the prior art include a photoconductor and a development electrode. The photoconductor surface is able to receive and maintain a selectively positioned electrical charge for attracting and positioning toner particles. During the development process, an electrical potential is applied to the development electrode providing an electrical field between the photoconductor surface and the development electrode. This electrical field serves two functions: first, the electrical field urges toner toward the latent electrostatic image on the photoconductor; secondly, the electrical field urges toner from the non-image areas of the photoconductor toward the development electrode and thereby cleans the background (i.e. non-image) areas on the photoconductor. Development electrodes have achieved widespread acceptance in the industry because they provide a continuous, even coat of toner to the entire image area, including solid image areas.
In known copying machines, the copying cycle is started by the placement of a charge on the photoconductor surface. When a toner fluid having negatively charged particles is utilized, this initial charge usually has a potential of +1000 volts and can be as high as +1400 volts. A latent electrostatic image is formed on the photoconductor surface by one of several methods which can include exposing the initial charge to an image forming 1ight source. The latent image area includes image portions which have the electrical potential of the initial charge and background or non-image portions which have a reduced electrical potential lower than that of the image areas.
The latent image on the photoconductor surface is passed in close proximity to the development electrode while toner fluid is pumped into the gap between the photoconductor surface and the development electrode. During this time, a low electrical potential having the same polarity as the photoconductor surface is applied to the development electrode. The potential applied to the development electrode is such that it creates an electrical field that enables the development of image areas and prevents the development of an image on the background areas. In a conventional electrostatic apparatus, when the image areas on the photoconductor surface have passed from the development electrode region, the polarity on the development electrode is reversed and the development electrode repels the charged toner particles deposited on the development electrode, thereby, pushing the toner particles back onto the photoconductor surface. The photoconductor surface is subsequently cleaned at a cleaning station located downstream with respect to the movement of the photoconductor surface.
The conventional systems employ photoconductors which must be maintained at high electrical potentials in order to provide clear copies at an acceptable rate.